Rethinking Grammar

I have been learning that I should not teach two similar concepts at the same time.
Unfortunately, grammar books in the teaching of Spanish as a foreign language present similar concepts in contrast.  This is standard methodology.

Now I know why students have such a difficult time mastering such concepts as:

Tú/Usted
Ser/Estar
Por/Para
Pretérito/Imperfecto

Clearly, this methodology was developed a long time ago, before we knew much about learning and the brain.

We, Spanish teachers, should be rethinking how key grammar concepts are being taught and develop new methodologies based on research and results.